Paleoenvironmental Records From Mud Area In The North Of East China Sea During Late Holocene

In this paper, marine paleoenvironmental evolvement during late Holocene was reconstructed from core FJ04 from north East China sea by using environmental proxies as AMS14C age dating, sensitive grain size group, long-chain unsaturated ketones and oxygen, carbon isotopes.Paleoenvironmental information since 3.6ka B.P. was recorded by the166cm-long core. Sensitive grain size analysis was taken from the upper 146cm of the core. The result shows that the mean size of the sensitive grain size group was influenced by East Asia Winter monsoon and the changing rout of the Yellow river. The research shows more than 11 strong East Winter Monsoon events during the last 3ka.Long-chain unsaturated ketones method to reconstruct SST is first introduced in the study area. By comparison, Global revise formula (Müller, 1998) is suitable for the study area. The result shows that the SST reconstructed by unsaturated ketones is annual SST for the study area. 0.75ka is an important turning point. SST reduced rapidly from 0.75ka B.P. till now. SST was high during 0.75 to 1.95ka B.P.. From 1.95 to 3.6ka B.P. SST is relatively stable.Benthic foraminifera Bolvina robusta was conducted oxygen and carbon analysis. The result shows very bad relativity between the oxygen and carbon isotopes, which related the complex marine dynamic environmental. 1.95ka B.P. is a turning point. The value for oxygen is very low from 1.95ka B.P. till now. The carbon isotope decreased by large extent only since the last 0.5 ka. All of this shows that the study area was strong influenced by Yellow sea coast current which has a characteristic of low temperature, low salinity and high nutrient during the late of late Holocene. From 1.95 ka B.P. to 3.6 ka B.P.,the study area was influenced by yellow sea warm current.Combination of the different proxies, we get paleoenvironmental evolvement of the study area since 3.6 ka B.P. This period can be devided in to four parts. 0.75 ka B.P. till now, East Asia Monsoon intensified, Yellow sea coast current influence increased. From 1.95 to 0.75 ka B.P., the East winter Monsoon weakened, Yellow sea warm current influence increased. Yellow sea coast current weakened. The study area was also influenced by Yellow river fresh water. From 1.95 to 3.6 ka B.P., East Asia Winter monsoon weakened as a whole, Yellow sea warm current intensified. Spectral analysis result from sensitive grain size and SST data shows that 1.5ka and 1.2ka millennial scale cycle. Centennial scale cycle as 86a, 110a, and 330a announced that solar activity was an important factor for the winter monsoon. SST variation was influenced not only by solar activity but the monsoon and current system evolvement.